Hydraulic circuit with filter control



Dec. 23, 1969 J. J. BERTA 3,435,363

HYDRAULIC CIRCUIT WITH FILTER CONTROL Filed Nov. 5, 1967 INVENTOR.

JAMES J. BERTA ATTORNEYS United States Patent Ofifice 3,485,368 Patented Dec. 23, 1969 US. Cl. 210-90 2 Claims ABSTRACT OF THE DISCLOSURE Apparatus for slowing a motor, having a hydraulic circuit including a pump, a hydraulic fluid filter, and a movable load, when the filter is clogged to indicate the clogged condition of the filter. The apparatus comprises means sensing a differential hydraulic pressure across the filter and means responsive to the differential pressure to reduce the hydraulic pressure exerted by the pump upon the load.

BACKGROUND OF THE INVENTION This invention relates to improved means for indicating the condition of a filter in a hydraulic motor.

The hydraulic circuits of many motors contain a filter which cleans the hydraulic fluid flowing within the circuit. A valved, filter bypass line is typically designed into the circuit. As contaminants accumulate on the filter, the pressure of the hydraulic fluid flowing to the filter begins to exceed that of the fluid flowing away from the filter. When the contaminants have accumulated to such a degree as to clog the filter, the pressure differential across the filter opens the bypass valve allowing the hydraulic fluid to bypass the filter. The fact that the filter is being bypassed is indicated on an instrument panel or the like which may be viewed by the motor operator. A vigilant operator should observe this indication, stop the motor, and replace the clogged filter with a clean one. Failure to do so will result in the hydraulic fluid being circulated throughout the hydraulic system without benefit of fluid filtration. Continued operation without filtration will contaminate the system and eventually damage one or more system components.

In practice, many operators do not observe an indicator of this nature for some time. Furthermore, many, pressed to complete the task at hand, will defer replacing the filter even while appreciating the need of doing so.

Briefly described, the present invention comprises apparatus for slowing a motor having a hydraulic circuit including a pump, a hydraulic fluid filter, and a movable load, when the filter is clogged to indicate the clogged condition of the filter. The apparatus comprises means sensing a ditferential hydraulic pressure across the filter and means responsive to the differential pressure to reduce the hydraulic pressure exerted by the pump upon the load.

Accordingly, it is a primary object of the present invention to provide a clogged filter indicator in a hydraulic motor which cannot be overlooked or ignored by the motor operator.

Another object of the invention is to provide a hydraulic circuit having a filter through which the circulating hydraulic fluid must pass regardless of the cleanliness of the fluid and a clogged filter indicator associated with the' circuit.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what are now considered to be the best modes contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a circuit diagram of a hydraulic motor illustrating one embodiment of the present invention. Two valves in the circuit are shown in cross-section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawing, there is schematically represented a circuit diagram of a hydraulic motor constructed in accordance with one embodiment of the present invention. An output line 10 having a pump 11 communicates between tank 12 and a movable piston 13 through an open-center type valve 14. In this embodiment, the movable piston is housed in a tilt cylinder in which the force of hydraulic fluid pressure is transferred to a mechanical linkage (not shown) by means of the rod 15. Tilt cylinders are commonly used as implements in heavy duty equipment such as tractors. A return line 16 communicates through valve 14 and a filter 17 to tank 12.

The hydraulic circuit also includes a system relief line 18 housing a system relief valve 19. This valve is of conventional design and operates in the following manner. Pressure fluid in system relief line 18 is communicated to a recessed portion 20 of a spring biased spool 21, reciprocally located in the system relief valve, and to a chamber 22 at the other end of spool 21 through an orifice 23. Thus, the pressures on each end of spool 21 are balanced and the position of the spool is determined by spring 24.

Under normal operating conditions spring 24 will urge spool 21 to the position shown so that fluid in system relief line 18 cannot be directed to tank 12 through a line 25. However, should the pressure in line 18 and chamber 22 become excessive, that pressure will force open a poppet type relief valve 30 and vent chamber 22 to tank 12 through a line 31. This in turn allows spool 21 to move to the right and establish communication between lines 18 and 25 causing part or all of the pump flow to be directed to the tank.

The hydraulic circuit also includes a filter bypass line 32 having a valve 33 which obstructs any flow of fluid therethrough while allowing the hydraulic pressure on each side of filter 17 to be exerted on opposite ends of a unitary spool 34 reciprocally located within the valve. Spool 34 is positioned by a spring 35 as illustrated under normal operating conditions. Valve 33 contains two annuli 36 adjacent spool 34 which communicate with lines 37 and 38, respectively. Line 37 communicates with output line 10 near a reduced diameter orifice 40 within the output line. Line 38 is also provided with a reduced diameter orifice 41 which communicates with an annulus 42 in valve 19 which leads to chamber 22.

Turning now to the operation of the motor, pump 11 forces hydraulic fluid from tank 12 through output line 10 to control valve 14. When the control valve is shifted to operate the load, fluid is directed into the left end of the tilt cylinder causing piston 13 to move to the right thereby expelling fluid from the right end of the cylinder into return line 16. The expelled fluid will then return through control valve 14 and filter 17 to tank 12. Whenever the control valve 14 is neutrally positioned, pump flow is caused to bypass the tilt cylinder through a conduit, not shown, within the control valve itself.

As the motor is used, contaminants will accumulate in filter 17 causing it to clog. As the degree of clogging increases, the pressure upstream from the filter in line 16 will exceed that downstream from the filter. This increase in pressure will also be transmitted to the left end of spool 34 in valve 33 through filter bypass line 32. At a predetermined point, the higher hydraulic pressure on the left or upstream end of the spool will overcome the combined hydraulic and spring pressure exerted on the right or downstream end causing spool 34 to move to the right. As this pressure differential increases and spool 34 continues its journey to the right, communication between annuli 36 will become established within valve 33 between the tWo land ends of spool 34. This in turn establishes communication between lines 37 and 38.

By virtue of the junction of line 37 with output line at a point just beyond orifice 40, which orifice has a smaller cross-sectional area than the output line itself, the hydraulic pressure downstream of the orifice and within line 37 'will become less than that in line 38 and chamber 22 which communicate with output line 10 through line 18 at a point upstream from the orifice. As a result, fluid will exit chamber 22 through line 38, valve 33, and into line 37. This is true regardless of the position of control valve 14. The rate at which chamber 22 is vented is regulated by an orifice 41 within line 38.

With the venting of chamber 22, the pressure therein will become less than that in the recessed portion of spool 21. As a consequence, spool 21 will move to the right and in doing so vent line 18 to the tank through line 25. This has the effect of decreasing the amount of fluid available in output line 10 for actuation of the movable piston 13. This in turn results in a slowing of the extension and retraction of rod 15.

A slowing of the implement connected to rod 15 is diflicult to overlook. Furthermore, it has a direct and diminutive bearing on the operators performance. In order to restore peak efficiency, he is forced to stop and change the filter. To finish the task at hand as swiftly as possible, the operator will change clogged filters rather than continue operation as has been the case with prior art systems.

It should be appreciated that many means may be used in reducing the flow of hydraulic fluid to the motor load in response to a pressure differential across a clogged filter. This may, for example, be accomplished by diversion of pump flow from the output line as in the case of the preferred embodiment. Alternatively, the pump itself may be slowed electrically in response to such a pressure drop. Then again, a valve may be placed within the output line in the vicinity of the load and gradually closed in such response.

While I have illustrated and described the preferred embodiments of my invention, it is to be understood that these are capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

What is claimed is:

1. A hydraulic circuit comprising a pump, a fluid motor supplied with pressure fluid from said pump for operating a mechanical implement, a fluid filter in the hydraulic circuit for filtering contaminants from said circuit and fluid pressure sensitive means in the hydraulic circuit for progressively slowing down the operation of said fluid motor in response to increased clogging of said filter by contaminants, said fluid pressure sensitive means comprising a first valve having a spool, one end of said first valve spool having fluid communication with pressure fluid upstream of said filter, a second end of said first spool having communication with pressure fluid downstream of said filter, a second valve in fluid communication with both said pump and said first valve and operable upon movement of said first valve spool to reduce the volume of fluid supplied from said pump to said motor, whereby clogging of said filter results in movement of said first valve spool which movement actuates said second valve and thereby reduces the volume of fluid supplied from said pump to said motor.

2. A hydraulic circuit as set forth in claim 1 and further comprising a reservoir, first conduit means communicating said reservoir with said pump, second conduit means communicating said pump with said fluid motor, said second conduit having a reduced diameter portion, said fluid filter located downstream of said fluid motor, third conduit means communicating said fluid motor with said fluid filter, fourth conduit means communicating pressure fluid upstream of said filter with said one end of said first valve spool, fifth conduit means downstream of said filter for communicating pressure fluid to said second end of said first valve spool, said second valve having a spring biased spool, sixth conduit means communicating a first end of said second valve spool with said first valve, seventh conduit means communicating a second end of the second valve spool with said second conduit at a location in said second conduit downstream of said pump and upstream of the reduced diameter portion of said second conduit, eighth conduit means communicating said second valve means with said reservoir, said spring biasing means normally urging said second valve spool to a position which blocks said seventh conduit from fluid communication with said eighth conduit, ninth conduit means communicating said first valve with said second conduit means at a location in said second conduit downstream of the reduced diameter portion of the second conduit, spring biasing means engaging said first valve spool for normally preventing fluid communication between said sixth and ninth conduits, whereby clogging of said filter increases the pressure in said fourth conduit and causes said first valve spool to move to a position communicating said sixth and ninth conduits and thereby actuating said second valve spool to a position communicating said seventh and eighth conduits which reduces the volume of fluid supplied from said pump to said motor and consequently slows the operation of the motor.

References Cited UNITED STATES PATENTS 2,566,633 9/1951 Rathmann 210-130 X 3,013,574 12/1961 Breting et al 2l0130 X 3,379,206 4/1968 Whiting 210130 X 3,410,411 11/1968 Dence 210 REUBEN FRIEDMAN, Primary Examiner JOHN W. ADEE, Assistant Examiner US. Cl. X.R. 

